Since an ethylene-α-olefin-non-conjugated diene copolymer rubber has excellent characteristics such as heat resistance, weatherability and ozone resistance, said copolymer rubber is used as a material for various uses such as automobiles, building materials, industrial materials and electric wires. Processing steps of said material have been rationalized, and as a result, they have been carried out in a short time because of severe cost competition.
In order to rationalize said processing steps, and as a result, carry out them in a short time, there has been proposed a conventional ethylene-α-olefin-non-conjugated diene copolymer rubber having a narrow molecular weight distribution or a low molecular weight. However, it has an unsatisfactory shape retaining property in an extrusion processing step, and as a result, it cannot make a required shape.
In order to improve a shape retaining property, there has been proposed another conventional ethylene-α-olefin-non-conjugated diene copolymer rubber having a wide molecular weight distribution to the contrary. However, it requires a long kneading time and gives an extruded material having an unsatisfactory surface because of insufficient kneading.
Accordingly, there has been needed an ethylene-α-olefin-non-conjugated diene copolymer rubber having an improved balance between kneading processability (kneadability in a short time) and a shape retaining property.
In response to said need, namely, in order to improve said balance, there has been proposed a further ethylene-α-olefin-non-conjugated diene copolymer rubber having a narrow molecular weight distribution and a special branch derived from a special diene as the fourth monomer (JP-W-2002-507228).
However, said copolymer rubber has to increase an amount of the branch in order to improve a shape retaining property, which deteriorates its kneading processability.